1. Field of the Invention
The invention relates to an electrochemical storage cell based on alkali metal and sulfur with at least one anode space and a cathode space which are separated from each other by an alkali ion-conducting solid electrolyte and are bounded at least in some areas by a housing and are provided with at least one anodic terminal element and a cathodic terminal element.
2. Description of the Prior Art
Such rechargeable electrochemical storage cells of the above type are used in high-temperature storage batteries which find use, for instance, as energy sources for electric motors.
Electrochemical storage cells of the alkali metal and chalcogen type which comprise an anode space and a cathode space which are separated from each other by an alkali-ion-conducting solid electrolyte, are eminently suitable for the construction of storage batteries of high energy and power density. The storage cells are preferably cup-shaped, i.e., they are bounded on the outside by a cup-shaped metallic housing and have in the interior a solid electrolyte which is likewise cup-shaped.
The dimensions of the solid electrolyte are chosen to provide a coherent space between its outer surfaces and the inner surfaces of the metallic housing. There are two kinds of storage cells: the normal storage cell and the inverted storage cell. In the normal storage cell, the cathode space is arranged between the solid electrolyte and the metallic housing while the anode space is in the interior of the cup-shaped solid electrolyte. In the inverted storage cell, the reagent spaces are arranged exactly in the reverse. The housings of these storage cells are preferably made of aluminum or steel. A disadvantage here that in particular, aluminum is corroded rapidly by the sulfur in the cathode space or by the sodium polysulfide formed during the discharge of the storage cell. In the storage cells known thus far, the metallic housing serves not only for delineating the storage cell, but also as an electric conductor. The sulfur in the cathode space brings about the formation of aluminum sulfide on the inside surfaces of the housing. Aluminum sulfide is an electric non-conductor, by means of the current flow through the storage cell is severely reduced. A further disadvantage is that the strength of the aluminum is decreased materially at a temperature of 350.degree. C.
If the housing is made of steel, its conductivity at a temperature of 350.degree. C. is very low. In this case, the ohmic resistance of the housing is 30% of the total resistance of the storage cell. While the electric conductivity can be increased by increasing the wall thickness of the housing, the total weight of the cell is increased, whereby the energy of such a storage cell referred to the weight is markedly reduced.